Control of patterned etching in semiconductor features

ABSTRACT

Copper can be pattern etched in a manner which provides the desired feature dimension and integrity, at acceptable rates, and with selectivity over adjacent materials. To provide for feature integrity, the portion of the copper feature surface which has been etched to the desired dimensions and shape must be protected during the etching of adjacent feature surfaces. To avoid the trapping of reactive species interior of the etched copper surface, hydrogen is applied to that surface. Hydrogen is adsorbed on the copper exterior surface and may be absorbed into the exterior surface of the copper, so that it is available to react with species which would otherwise penetrate that exterior surface and react with the copper interior to that surface. Sufficient hydrogen must be applied to the exterior surface of the etched portion of the copper feature to prevent incident reactive species present due to etching of adjacent feature surfaces from penetrating the previously etched feature exterior surface. The most preferred embodiment of the invention provides for the use of hydrogen chloride (HCl) and/or hydrogen bromide (HBr) as the sole or principal source of the reactive species used in etching copper. Dissociation of the HCl and/or HBr provides the large amounts of hydrogen necessary to protect the copper feature etched surfaces from penetration by reactive species adjacent the etched surface. Additional hydrogen gas may be added to the plasma feed gas which comprises the HCl and/or HBr when the reactive species density in the etch process chamber is particularly high. Although the HCl or HBr may be used as an additive in combination with other plasma feed gases, preferably HCl or HBr or a combination thereof accounts for at least 40%, and more preferably at least 50%, of the reactive species generated by the plasma. Most preferably, HCl or HBr should account for at least 80% of the reactive species generated by the plasma.

This application is a divisional application of U.S. application Ser.No. 09/393,446, filed Aug. 9, 1999, now allowed, which is a continuationapplication of U.S. application Ser. No. 08/911,878, filed Aug. 13,1997, and issued as U.S. Pat. No. 6,008,140 on Dec. 28, 1999.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention pertains to a particular chemistry which providesadvantages in the pattern etching a copper layer on the surface of asemiconductor device substrate. In particular, the etched portion of afeature surface is protected from reactive species during the etching ofadjacent feature surfaces.

2. Brief Description of the Background Art

In the multi level metallization architecture used in present daysemiconductor devices, aluminum is generally used as the material ofconstruction for interconnect lines and contacts. Although aluminumoffers a number of advantages in ease of fabrication, as integratedcircuit designers focus on transistor gate velocity and interconnectline transmission time, it becomes apparent that copper is the materialof choice for the next generation of interconnect lines and contacts. Inparticular, when the aluminum wire size becomes smaller than 0.5 μm, theelectromigration resistance and the stress migration resistance ofaluminum becomes a problem area. In addition, when the feature size ofan aluminum-based contact requires an aspect ratio of greater than 1:1,it is difficult to obtain planarization of the substrate during theapplication of the next insulating layer over the contact area of thesubstrate. Further, the resistivity of copper is about 1.4 μΩcm, whichis only about half of the resistivity of aluminum.

There are two principal competing technologies under evaluation bymaterial and process developers working to enable the use of copper. Thefirst technology is known as damascene technology. In this technology, atypical process for producing a multilevel structure having featuresizes in the range of 0.5 micron (μm) or less would include: blanketdeposition of a dielectric material; patterning of the dielectricmaterial to form openings; deposition of a diffusion barrier layer and,optionally, a wetting layer to line the openings; deposition of a copperlayer onto the substrate in sufficient thickness to fill the openings;and removal of excessive conductive material from the substrate surfaceusing chemical-mechanical polishing (CMP) techniques. The damasceneprocess is described in detail by C. Steinbruchel in “Patterning ofcopper for multilevel metallization: reactive ion etching andchemical-mechanical polishing”, Applied Surface Science 91 (1995)139-146.

The competing technology is one which involves the patterned etch of acopper layer. In this technology, a typical process would includedeposition of a copper layer on a desired substrate (typically adielectric material having a barrier layer on its surface); applicationof a patterned hard mask or photoresist over the copper layer; patternetching of the copper layer using wet or dry etch techniques; anddeposition of a dielectric material over the surface of the patternedcopper layer, to provide isolation of conductive lines and contactswhich comprise various integrated circuits. An advantage of thepatterned etch process is that the copper layer can be applied usingsputtering techniques well known in the art The sputtering of copperprovides a much higher deposition rate than the evaporation or CVDprocesses typically used in the damascene process, and provides a muchcleaner, higher quality copper film than CVD. Further, it is easier toetch fine patterns into the copper surface and then deposit aninsulating layer over these patterns than it is to get the barrier layermaterials and the copper to flow into small feature openings in the topof a patterned insulating film.

Each of the above-described competing technologies has particularprocess problems which must be solved to arrive at a commerciallyfeasible process for device fabrication. In the case of the damasceneprocess, due to difficulties in the filling of device feature sizes of0.25 μm and smaller (and particularly those having an aspect ratiogreater than one) on the surface of the dielectric layer, the method ofchoice for copper deposition is evaporation (which is particularly slowand expensive); or chemical vapor deposition, or CVD (which produces acopper layer containing undesirable contaminants and is also arelatively slow deposition process). Just recently, electroplating hasbeen investigated as a method for copper deposition.

Regardless of the technique used to deposit copper, the CMP techniquesused to remove excess copper from the dielectric surface afterdeposition create problems. Copper is a soft material which tends tosmear across the underlying surface during polishing. “Dishing” of thecopper surface may occur during polishing. As a result of dishing, thereis variation in the critical dimensions of conductive features.Particles from the slurry used, during the chemical mechanical polishingprocess may become embedded in the surface of the copper and othermaterials surrounding the location of the copper lines and contacts. Thechemicals present in the slurry may corrode the copper, leading toincreased resistivity and possibly even corrosion through an entire wireline thickness. Despite the number of problems to be solved in thedamascene process, this process is presently viewed in the industry asmore likely to succeed than a patterned copper etch process for thefollowing reasons.

The patterned etch process particularly exposes the copper to corrosion.Although it is possible to provide a protective layer over the etchedcopper which will protect the copper from oxidation and other forms ofcorrosion after pattern formation, it is critical to protect the copperduring the etch process itself to prevent the accumulation of involatilecorrosive compounds on the surface of the etched copper features. Theseinvolatile corrosive compounds cause continuing corrosion of the coppereven after the application of a protective layer over the etchedfeatures.

Wet etch processes have been attempted; however, there is difficulty incontrolling the etch profile of the features; in particular, when thethickness of the film being etched is comparable to the, minimum patterndimension, undercutting due to isotropic etching becomes intolerable. Inaddition, there is extreme corrosion of the copper during the etchprocess itself.

Plasma etch techniques provide an alternative. A useful plasma etchprocess should have the following characteristics: It should be highlyselective against etching the mask layer material; it should be highlyselective against etching the material under the film being etched; itshould provide the desired feature profile (e.g. the sidewalls of theetched feature should have the desired specific angle); and the etchrate should be rapid, to maximize the throughput rate through theequipment.

Until very recently etch rates obtained by purely physical bombardmentwere typically about 300 Å-500 Å per minute or less, as described bySchwartz and Schaible, J. Electrochem. Soc., Vol. 130, No. 8, p. 1777(1983) and by H. Miyazaki et al., J. Vac. Sci. Technol. B 15(2) p.239(1997), respectively. Recently, applicants have been able to improve onthe etch rates achievable by purely physical bombardment so that etchrates as high as 5,000 Å per minute can be achieved. Further, theselectivity between copper and materials commonly used as barrierlayers, insulating layers and patterning masks is more thansatisfactory. This technology is disclosed in detail in U.S. Pat. No.6,010,603, issued to Ye et al. on Jan. 4, 2000. However, etch rate andselectivity must be accompanied by the ability to etch a pattern havingthe desired cross-sectional profile. To improve etch profile, it isnecessary to use a limited amount of chemical reactants during the etchprocess.

The chemical reactants must be very carefully selected to react with thecopper and create volatile species which can then be removed byapplication of vacuum to the process chamber. However, when suchchemical reactants are used, corrosion is a major problem during thefabrication, as copper does not form any self passivating layer likealuminum does. In particular, oxidation of copper increases resistivity;further, in the case of copper interconnect lines, the whole wire linemay corrode all the way through, resulting in device failure. Asdescribed in U.S. Pat. No. 6,010,603, referenced above, it is possibleto use a limited concentration of particular halogen-based reactants incombination with physical bombardment, when physical bombardment is thecontrolling etch mechanism and avoid corrosion of the copper by thereactive species used to assist in the etch process.

There are some etch profiles for which etching in the physicalbombardment regime does not provide the best result. In addition,applicants have discovered that it is possible to obtain etch rateswhich are higher than those obtained to date in the physical bombardmentregime and still avoid corrosion of the etched copper. Typically, achlorine-comprising gas is used in the reactive ion etch processing ofthe copper. Although the chlorine provides acceptable etch rates, itcauses the copper to corrode rapidly. The chlorine reacts very fast, butproduces reaction by-products which are not volatile. These byproductsremain on the copper surface, causing corrosion over the entire etchedsurface. The byproducts can be made volatile subsequent to the etch stepby treatment with chemical species which create a volatile reactionproduct, but by this time the corrosion is already extensive.

An example of a treatment to remove chlorides and fluorides remainingafter the etch of a conductive layer is provided in U.S. Pat. No.4,668,335 to Mockler et al., issued May 26, 1987. In Mockler et al., theworkpiece (wafer) is immersed in a strong acid solution, followed by aweak base solution after the etch of an aluminum-copper alloy, to removeresidual chlorides and fluorides remaining on the surface after etching.Another example is provided in U.S. Pat. No. 5,200,031 to Latchford etal., issued Apr. 6, 1993. In Latchford et al, a process is described forremoving a photoresist remaining after one or more metal etch stepswhich also removes or inactivates chlorine-containing residues, toinhibit corrosion of remaining metal for at least 24 hours.Specifically, NH₃ gas is flowed through a microwave plasma generatorinto a stripping chamber containing the workpiece, followed by O₂ gas(and optionally NH₃ gas), while maintaining a plasma in the plasmagenerator.

Attempts have been made to reduce the corrosion by introducingadditional gases during the etch process (which can react with thecorrosion causing etch byproducts as they are formed). In addition,gaseous compounds which can react to form a protective film over thesidewalls of etched features as they are formed have been added duringthe etching process and after the etch process. However, residualcorrosion continues to be a problem and the protective film, whileprotecting from future contact with corrosive species, may trapcorrosive species already present on the feature surface.

An example of the formation of a passivating film on pattern sidewallsis presented by J. Torres in “Advanced copper interconnections forsilicon CMOS technologies”, Applied Surface Science, 91 (1995) 112-123.Other examples are provided by Igarashi et al. in: “High ReliabilityCopper Interconnects through Dry Etching Process”, Extended Abstracts ofthe 1994 International Conference on Solid State Devices and Materials,Yokohama, 1994, pp.943-945; in “Thermal Stability of Interconnect ofTiN/cutin Multilayered Structure”, Jpn. J. Appl. Phys. Vol. 33 (1994)Pt. 1, No. 1B; and, in “Dry Etching Technique for Subquarter-MicronCopper Interconnects”, J. Electrochem. Soc., Vol. 142, No. 3, March1995. In this 1995 article, Yasushi Igarashi et al. showphotomicrographs of cross-sectional views of the subquarter-micronetched features. In reviewing the article, applicants noticed thatalthough the exterior walls of the feature appear to be solid, thereappears to be interior hollow areas within the feature where the copperline has been eroded away. Applicants subsequently reproduced thiseffect, demonstrated by the comparative example (Example 3) presentedsubsequently herein. Apparently, reactive chlorine species are trappedinterior to the passivating film formed on the wall and these speciesreact with and erode the copper beneath the passivating film.

Passivating films are used to protect the walls of forming featuresduring the etching of aluminum. Such films are generally used to protectthe walls of etched features from further etching by incident reactivespecies during continued vertical etching of the feature through a mask.Typically the protective film comprises an oxide or a nitride or apolymeric material, or a combination thereof. In the case of aluminum,aluminum oxide forms a cohesive, continuous protective film veryrapidly. This rapid formation of a continuous protective film protectsthe interior of the etched feature from exposure to significant amountsof the reactive species which could cause corrosion interior to theetched wall. However, in the case of copper, there is no similarrapidly-formed film which prevents reactive species from reaching thecopper surface and being trapped there by a slowly-formed “passivating”film. It appears that the passivating films of the kind described byIgarashi et al. in their March 1995 article trap reactive species insidethe feature walls and these reactive species corrode away the copperinterior to the feature walls.

If the patterned etch technique is to be used for fabrication ofsemiconductor devices having copper interconnects, contacts, andconductive features in general, it is necessary to find an etch methodwhich does not create immediate corrosion or a source of futurecorrosion.

In addition to controlling corrosion, it is necessary to control theprofile of the etched pattern. An example of a technique used forobtaining a high etch rate and highly directional reactive etching ofpatterned copper films copper is described by Ohno et al in “ReactiveIon Etching of Copper Films in a SiCl₄, N₂, Cl₂, and NH₃ Mixture”, J.Electrochem. Soc., Vol. 143, No. 12, December 1996. In particular, theetching rate of copper is increased by increasing the Cl₂ flow rate attemperatures higher than 280° C. However, the addition of Cl₂ is said tocause undesirable side etching of the Cu patterns. NH₃ is added to thegas mixture to form a protective film that prevents side wall etching.The etch gas mixture which originally contained SiCl₄ and N₂ wasmodified to contain SiCl₄, N₂, Cl₄, and NH₃.

Thus, protective films formed during etching are used by somepractitioners skilled in the art to reducing corrosion (as describedabove) and by others for controlling the directional etching of thepattern surface. In either case, although the formation of such aprotective film may work well for aluminum etching, it may be harmful inthe case of copper etching for the reasons previously described.

Toshiharu Yanagida, in Japanese Patent Application No. 4-96036,published Oct. 22, 1993, describes a method of dry etching of a coppermaterial in the temperature range at which a polymeric resist mask canbe used (below about 200° C.). Etching using a polymeric resist mask issaid to be preferable so that the presence of oxygen (present in asilicon oxide hard masking material which can withstand highertemperatures) can be avoided. The oxide causes harmful corrosion of thecopper, producing copper oxides which increase the resistivity of etchedcopper features. In particular, the Yanagida reference describes the useof hydrogen iodide (HI) gas and combinations of HI gas with chlorideand/or fluoride compounds to achieve etching at substrate temperaturesbelow about 200° C.

FIGS. 5A and 5B illustrate the kind of corrosion which typically isexperienced during the reactive ion etching of copper. The patternetched was one of lines and spaces, wherein the lines and spaces wereapproximately 0.5 μm in width looking at a cross-sectional profile ofthe pattern. The details of the preparation of the etched substratesshown in FIGS. 5A and 5B will be discussed in detail subsequentlyherein, for comparative purposes. For now, the important features tonote are that the copper lines 510 which appear to be solid looking atthe exterior walls 516 are actually hollow in the interior, where thecopper 520 remaining after etching is surrounded by vacant space 522.The vacant space is created by the harmful copper reactions we arecalling “corrosion”. Corrosion is caused when the copper reacts withoxygen or with other reactants present in the process vessel to produceundesirable by-products. Corrosion also includes reaction with halogenswhich are typically used as etchant reactants, but the reaction occursat an undesired rate so that the desired etched feature profile cannotbe obtained. FIGS. 5A and 5B are representative of this latter case.

We have discovered a particular etch chemistry which makes it possibleto etch micron and submicron sized copper features on a semiconductorsubstrate while maintaining the integrity of the etched copper feature.

SUMMARY OF THE INVENTION

We have discovered that copper can be pattern etched in a manner whichprovides the desired feature dimension and integrity, at acceptablerates, and with selectivity over adjacent materials. To provide forfeature integrity, the portion of the copper feature surface which hasbeen etched to the desired dimensions and shape must be protected duringthe etching of adjacent feature surfaces. This is particularly importantfor feature sizes less than about 0.5 μm, where presence of even alimited amount of a corrosive agent can eat away a large portion of thefeature. To avoid the trapping of reactive species which can act as acorrosive agent interior of the etched copper surface, hydrogen isapplied to that surface. Hydrogen is adsorbed on the copper exteriorsurface and may be absorbed into the exterior surface of the copper, sothat it is available to react with species which would otherwisepenetrate that exterior surface and react with the copper interior tothat surface. Sufficient hydrogen must be applied to the exteriorsurface of the etched portion of the copper feature to prevent incidentreactive species present due to etching of adjacent feature surfacesfrom penetrating the previously etched feature exterior surface.

Although any plasma feed gas component comprising hydrogen, which iscapable of generating sufficient amounts of hydrogen, may be used, themost preferred embodiment of the invention provides for the use of acomponent which contains both hydrogen and halogen. Preferred examplesare hydrogen chloride (HCl) and/or hydrogen bromide (HBr), which areused as the principal source of the reactive species for etching copper.Dissociation of the HCl and/or HBr provides large amounts of hydrogenfor protection of etched copper surfaces, thereby preventing penetrationby reactive species adjacent the etched surface. Additional hydrogen gasmay be added to the plasma feed gas which comprises the HCl and/or HBrwhen the reactive species density in the etch process chamber isparticularly high. The hydrogen-releasing, halogen-comprising plasmafeed gas component may be used as an additive (producing less than 40%of the plasma-generated reactive species) in combination with otherplasma etching species.

When HCl and/or HBr is used as the principal source of reactive speciesfor the copper etching, the HCl or HBr accounts for at least 40%, andmore preferably at least 50%, of the reactive species generated by theplasma. Most preferably, HCl or HBr accounts for at least 80% of suchreactive species. Other reactive species may be used for purposes offeature surface passivation during etching or for purposes of featuresurface protection after completion or near the completion of featuresurface etching. The species added for surface passivation or surfaceprotection during etching of the copper feature preferably make up 30%or less, or more preferably make up 10% or less of the plasma-generatedreactive species.

In particular, the preferred method for the patterning of copper on asubstrate surface includes the following steps:

a) supplying to a plasma etch process chamber a plasma feed gasincluding hydrogen in the form of HCl, or HBr, or H₂, or a combinationthereof, in an amount which provides plasma-generated dissociatedhydrogen in an amount sufficient to form a protective layer over anexterior portion of a copper feature which has been etched to thedesired dimensions; and

b) etching said copper features to provide said desired pattern.

In addition to including additional species-generating gases forpurposes of passivating various surfaces and reacting with potentiallycorrosive species on the semiconductor substrate, such as oxygen,gaseous hydrogen-containing molecules may be used to adjust the ratio ofhydrogen to halogen in the plasma. By way of example, additional gaseswhich may be added to the plasma feed gas include CH₄, CH₃F, BCl₃, N₂,NH₃, SiCl₄, CCl₄, and CHF₃.

Plasma feed gases may include additional inert (non-reactive withcopper) gases such as argon, helium, or xenon, to enhance theionization, or dissociation, or to dilute the reactive species.

In a particularly preferred embodiment of the present invention, copperis patterned on a substrate surface for use in semiconductorfabrication, wherein the method steps comprise:

a) supplying a plasma feed gas to a plasma etch process chamber, orother controlled environment for the production of a plasma, whereinsaid feed gas includes HCl, or HBr, or H₂, or a combination thereof,wherein the amount of HCl or HBr is sufficient that at least 40%, andpreferably at least 50%, of the total reactive species present in theplasma are supplied by the HCl or HBr or combination thereof;

b) using a plasma created from the plasma feed gas in a manner whichprovides a reactive species density sufficient to enable a copper etchrate of at least about 2,000 Å per minute.

The amount of H₂ gas added to the feed gas will depend on the density ofreactive species present at the surface of the copper during etching.Hydrogen gas may be added to the plasma feed gas for only a portion ofthe feature etch time period.

As previously mentioned, other gases capable of generating reactivespecies for purposes of surface passivation or as an oxygen “getter” ,such as N₂ or BCl₃, respectively, may be used in the plasma feed gas. Inaddition, inert gases such as argon may be used.

The critical feature is the availability of hydrogen at the featuresurface during the etching process. The use of HCl or HBr as the primarysource of the copper etchant reactive species provides for theavailability of dissociated, reactive hydrogen, as the hydrogen isreleased upon creation of the plasma and is adsorbed on or absorbed nearthe copper surface during etching, where it buffers the reaction of thechlorine or bromine species with the copper surface which is beingetched. This protects the interior of the copper feature from subsequentcorrosion while permitting etch rates for adjacent copper surfaces of atleast 2,000 Å per minute. To enhance this protection of the etchedcopper feature surface, hydrogen may be provided from plasma-generatedspecies

When the etch process is carried out typically oxygen-comprising speciesare generated from a silicon oxide hard mask or a photoresist, or froman insulating layer present on the substrate. Under these circumstances,it is advantageous to add boron trichloride (BCl₃) or an equivalentoxygen scavenger.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustrating a decoupled plasma source (DPS)etching chamber of the kind used during the patterned etching of copperas described in the preferred embodiments of the present invention.

FIG. 2A illustrates the change in copper intensity in the etch plasmaduring the etching of a pattern of 0.5 μm wide lines and spaces into thesurface of a copper film, where the principal source for thecopper-etching reactive species is HCl.

FIG. 2B illustrates the change in copper intensity in the etch plasmaduring the etching of a pattern of 0.5 μm wide lines and spaces into thesurface of a copper film, where the principal source for thecopper-etching reactive species is HBr.

FIG. 3A illustrates the etch rate in μm per minute for a pattern of 0.5μm wide lines and spaces into the surface of a copper film, as afunction of etch chamber pressure. The feed gas to the etch chamberincluded HCl, N₂, and BCl₃.

FIG. 3B illustrates the etch rate for the same patterned copper film asthat described with reference to FIG. 3A, but as a function of sourcepower.

FIG. 3C illustrates the etch rate for the same patterned copper film asthat described with reference to FIG. 3A, but as a function of biaspower.

FIG. 4A illustrates the selectivity of copper relative to the patterningmask, shown as the ratio of copper etch rate to silicon oxide etch ratefor a standard test pattern of various width lines and spaces, as afunction of etch chamber pressure.

FIG. 4B illustrates the selectivity of copper relative to patterningmask, shown as the ratio of copper etch rate to silicon oxide etch ratefor the same test pattern as that described with reference to FIG. 4A,but as a function of source power.

FIG. 4C illustrates selectivity of copper relative to patterning mask,shown as the ratio of copper etch rate to silicon oxide etch rate forthe same test pattern as that described with reference to FIG. 4A, butas a function of bias power.

FIG. 5A is a three dimensional schematic of a copper film which wasreactive ion etched using Cl₂, BCl₃, N₂, and Ar to produce a pattern of0.5 μm wide lines and spaces. Although the integrity of the etchedcopper lines appears to be good on the surface, large portions of theinterior of the copper lines is vacant space from reacted copper whichhas exited.

FIG. 5B is a schematic of the cross-sectional view of the FIG. 5A etchedcopper pattern, showing additional detail of the structure of theinterior of the etched copper line.

FIG. 6A is a three dimensional schematic of a copper film which wasreactive ion etched using a preferred embodiment method of the presentinvention. The integrity of the interior of the etched copper lines isexcellent.

FIG. 6B is a schematic of the cross-sectional view of FIG. 5A etchedcopper pattern, showing additional detail of the structure of theinterior of the etched copper line.

FIG. 6C is a schematic of the FIG. 5A etched copper pattern which showsthe top surface of the etched lines (as well as the front edge) and thetop surface of the etched spaces, to illustrate the absence of anydeposits on the exterior of the etched lines and spaces.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

We have discovered that copper can be pattern etched in a manner whichprovides the desired feature dimension and integrity, at acceptablerates, and with selectivity over adjacent mask materials. To provide forfeature integrity, the portion of the copper feature surface which hasbeen etched to the desired dimensions and shape must be protected duringthe etching of adjacent feature surfaces. To avoid the trapping ofreactive species interior of the etched copper surface, hydrogen isapplied to that surface. The most preferred embodiment of the inventionprovides for the use of hydrogen chloride (HCl) and/or hydrogen bromide(HBr) as the sole or principal source of the reactive species used inetching copper. Dissociation of the HCl and/or HBr provides the largeamounts of hydrogen necessary to protect the copper feature etchedsurfaces from penetration by reactive species adjacent the etchedsurface. Additional hydrogen gas may be added to the plasma feed gaswhich comprises the HCl and/or HBr when the reactive species density inthe etch process chamber is particularly high.

I. Definitions

As a preface to the detailed description, it should be noted that, asused in this specification and the appended claims, the singular forms“a”, “an”, and “the” include plural referents, unless the contextclearly dictates otherwise. Thus, for example, the term “asemiconductor” includes a variety of different materials which are knownto have the behavioral characteristics of a semiconductor, reference toa “plasma” includes a gas or gas reactants activated by a glowdischarge, and a reference to “copper” includes alloys thereof.

Specific terminology of particular importance to the description of thepresent invention is defined below.

The term “anisotropic etching” refers to etching which does not proceedin all directions at the same rate. If etching proceeds exclusively inone direction (e.g. only vertically), the etching process is said to becompletely anisotropic.

The term “aspect ratio” refers to the ratio of the height dimension tothe width dimension of particular openings into which an electricalcontact is to be placed. For example, a via opening which typicallyextends in a tubular form through multiple layers has a height and adiameter, and the aspect ratio would be the height of the tubulardivided by the diameter. The aspect ratio of a trench would be theheight of the trench divided by the minimal travel width of the trenchat its base.

The term “bias power” refers to the power used to control ionbombardment energy and the directionality of ions toward a substrate.

The term “copper” refers to copper and alloys thereof, wherein thecopper content of the alloy is at least 80 atomic % copper. The alloymay comprise more than two elemental components.

The term “feature” refers to metal lines and openings on a substrate,and other structures which make up the topography of the substratesurface.

The term “glow discharge sputtering” refers to a mechanism in whichatoms are dislodged from a surface which is to be sputtered, bycollision with high energy particles which are generated by a glowdischarge, where the glow discharge is a self-sustaining type of plasma.The high energy particles may be energetic atoms as well as energeticmolecules.

The term “ion bombardment” refers to physical bombardment by ions (andother excited species of atoms which are present with the ions) toremove atoms from a surface, where physical momentum transfer is used toachieve the atom removal.

The term “isotropic etching” refers to an etching process where etchingcan proceed in all directions at the same rate.

The term “plasma” refers to a partially ionized gas containing an equalnumber of positive and negative charges, as well as some other number ofnon-ionized gas particles.

The term “source power” refers to the power used to generate ions andneutrals whether directly in an etching chamber or remotely as in thecase of a microwave plasma generator.

The term “substrate” includes semiconductor materials, glass, ceramics,polymeric materials, and other materials of use in the semiconductorindustry.

II. An Apparatus for Practicing the Invention

The etch process was carrier out in a Centura® Integrated ProcessingSystem available from Applied Materials, Inc. of Santa Clara, Calif. Thesystem is shown and described in U.S. Pat. No. 5,186,718, the disclosureof which is hereby incorporated by reference. This equipment included aDecoupled Plasma Source (DPS) of the kind described by Yan Ye et al. atthe Proceedings of the Eleventh International Symposium of PlasmaProcessing, May 7, 1996 and as published in the Electrochemical SocietyProceedings, Volume 96-12, pp. 222-233 (1996) which is herebyincorporated by reference. The plasma processing chamber enables theprocessing of an 8 inch (200 mm) diameter silicon wafer while providingcontrol over critical dimension variation.

As described in the Yan Ye et al. paper referenced above, metal etch isan ion enhanced chemical process, and in addition to selecting a properprocess gas, it is also necessary to control a number of processparameters such as bias power, source power, pressure, flow rate andwafer temperature. Wafer temperature is a function of plasma sourcepower and helium (heat transfer gas) pressure at the backside of a wafer(substrate), as well as other variables. A higher He pressure (for anon-heated electrostatic chuck), lowers the substrate surfacetemperature. Uniform wafer temperature is achieved through optimizationof electrostatic chuck design and cathode design. Wafer temperature isimportant since critical dimension variation is sensitive to a change inwafer temperature. This indicates that feature sidewall passivation isan important mechanism for critical dimension control.

A schematic of the processing chamber is shown in FIG. 1A which shows anetching process chamber 10, which is constructed to include at least oneinductive coil antenna segment 12 positioned exterior to the etchprocess chamber 10 and connected to a radio frequency (RF) powergenerator 18. Interior to the process chamber is a substrate 14 supportpedestal 16 which is connected to an RF frequency power generator 22through an impedance matching network 24, and a conductive chamber wall30 which serves as the electrical ground 34 for the offset bias whichaccumulates on the substrate 14 as a result of the RF power applied tothe substrate support pedestal 16.

The semiconductor substrate 14 is placed on the support pedestal 16 andgaseous components are fed into the process chamber through entry ports26. A plasma is ignited in process chamber 10 using techniques wellknown in the industry. Pressure interior to the etch process chamber 10is controlled using a vacuum pump (not shown) and a throttle valve 27connected to a process chamber gas exit line 28. The temperature on thesurface of the etch chamber walls is controlled using liquid-containingconduits (not shown) which are located in the walls of the etch chamber10. The temperature of the semiconductor substrate was controlled bybombarding the surface of the substrate with an argon plasma to reachinitial temperature and subsequently, during the etch process by impactof plasma species on the substrate surface. For experimental purposes,it was desired to maintain the substrate temperature above about 150° C.and below about 350° C., which we were able to do relying solely uponsurface bombardment of the substrate. The surface of the etching chamber10 walls was maintained at about 80° C. using the cooling conduitspreviously described. In the case of a production process, preferably,the substrate support platen provides for backside heating or cooling ofthe substrate.

III. Achieving Patterned Copper Etch Using the Method of the PresentInvention

The Examples provided below for the etching of patterned copper werepracticed in the Centura® Integrated Processing System previouslydescribed.

The substrate was a silicon wafer overlaid by a silicon oxide dielectriclayer. Typically, a 500 Å thick barrier layer of tantalum was appliedover the silicon oxide dielectric layer. A 5,000 Å thick layer of copperwas sputter deposited over the barrier layer. A 250 Å thick layer oftantalum was applied over the copper layer, and a 5,000 Å thickpatterned silicon oxide hard mask was applied over the tantalum layer.When the substrate varied from this general description, the variance isspecified in the particular preferred embodiment described.

A plasma was created in the etch chamber using standard techniques, withthe composition of the plasma feed gas being as specified. The power tothe external RF coil is specified for each Example, with the frequencybeing about 2 MHz in all cases. A substrate offset bias was created byapplication of RF power at a frequency of about 13.56 MHz and a wattageabove about 50 W (equivalent to a bias voltage of about 20 V).Preferably the power to the support platen ranges from about 400 W toabout 800 W.

The pressure in the etch chamber ranged between about 0.1 mT to 100 mT,and was preferably below about 20 mT. The temperature on the substratesurface ranged from about 130° C. to about 300° C., while the walltemperature of the etch chamber was preferably at least 50 degrees lowerthan the substrate temperature. Typically the etch chamber surface wasmaintained at about 80° C. or less.

EXAMPLE ONE Etch Rate

FIG. 2A shows the etch rate curve 210 for the etching of a copper filmto form a pattern of 0.35 μm wide lines and spaces using HCl as theprincipal source of copper etchant reactive species. In particular, thebase of the substrate etched was a silicon wafer having a thermal oxidecoating on its surface. A 500 Å thick layer of tantalum was applied overthe thermal oxide; a 18,000 Å thick layer of copper was applied over thetantalum layer; a 250 Å thick tantalum nitride layer was applied overthe copper layer; and, finally, a silicon oxide hard mask 5,000 Å thickwas applied over the tantalum nitride layer.

This stack of materials was etched in the Centura® Integrated ProcessingSystem previously described. The plasma feed gas to the process chamberwas 100 sccm of HCl, 25 sccm of N₂, and 5 sccm BCl₃. The substratetemperature during etching was about 200° C., with the process chamberwalls at about 80° C. The process chamber pressure during etching was 20mT. The source power to the plasma inducing coil was about 1,500 W @ 2MHz and the bias power to the substrate support platen was about 500 W @13.56 MHz. A plasma was ignited using techniques standard in the art,and the presence of any copper emissions in the plasma were monitoredusing an optical sensor measuring at a wavelength of about 3,250 Å. FIG.2A shows the optical emission intensity 212 for copper appearing in theplasma, as a function of time 214 in seconds. At about 90 seconds, theintensity of the copper in the plasma began dropping, indicating thatthe copper etching area was depleting. Since etching is slower is someareas than in others, the copper in the plasma gradually decreased, andthe curve 210 leveled out at about 120 seconds, indicating that the etchwas completed in all areas. Applicants believe the average time forcompletion of etching to be about 105 seconds. Using 105 seconds as thetime for completion of etching, the calculated etch rate is about 10,000Å per minute or about 1.0 μm per minute.

FIG. 2B shows the etch rate curve 220 for the etching of a copper filmto form a pattern of 0.35 μm wide lines and spaces using HBr as theprincipal source of copper etchant reactive species. In particular, thebase of the substrate etched was a silicon wafer having a thermal oxidecoating on its surface. A 500 Å thick layer of tantalum was applied overthe thermal oxide; a 5,000 Å thick layer of copper was applied over thetantalum layer; a 250 Å thick tantalum nitride layer was applied overthe copper layer; and, finally, a silicon oxide hard mask 5,000 Å thickwas applied over the tantalum nitride layer.

This stack of materials was etched in the Centura® Integrated ProcessingSystem previously described. The plasma feed gas to the process chamberwas 100 sccm of HBr, 25 sccm of N₂, and 5 sccm BCl₃. The substratetemperature during etching was about 200° C., with the process chamberwalls at about 80° C. The process chamber pressure during etching was 20mT. The source power to the plasma inducing coil was about 1,500 W andthe bias power to the substrate support platen was about 500 W. A plasmawas ignited using techniques standard in the art, and copper emissionsappearing in the plasma were monitored using an optical sensor measuringat a wavelength of about 3,250 Å. FIG. 2B shows the optical emissionintensity reading 222 for the copper appearing in the plasma, as afunction of time 224 in seconds. Since a pattern was etched, again, thecompletion of copper etch was indicated, by a drop in the copperintensity reading over time. At the end of 20 seconds, the amount ofcopper began to drop, indicating that the majority of the etching wascomplete, with curve 220 leveling out to show no copper generated atabout 30 seconds. Applicants believe the average time for completion ofetching to be about 25 seconds. Using 25 seconds as the time forcompletion of etching, the calculated etch rate is about 12,000 Å perminute or about 1.2 μm per minute.

As a part of determining the effect of process variables on etch rate,the effect of process chamber pressure, plasma source power, and biaspower were investigated. In particular, HCl was the principal source ofetchant reactive species; the plasma feed gas was of the compositionspecified with reference to FIG. 2A above; the substrate stack was thesame; the pattern etched was the same; and all process variables werethe same with the exception of the variable investigated.

As a matter of importance, the preferred embodiments described abovewere carried out at a substrate temperature of about 200° C., andpreferably the process is carried out at a temperature of at least about200° C. However, the process works at temperatures above about 130° C.We have yet to determine the highest recommended temperature; however,one skilled in the art will appreciate that at higher temperatures othermaterials within the substrate are affected, thermal expansiondifferences can cause problems, and that there needs to be anoptimization of substrate temperature depending on the device and thefeature being fabricated. In any case, the substrate temperature shouldnot exceed about 400° C.

Curve 310 of FIG. 3A shows the etch rate 312 as a function of processchamber pressure 314, with the etch rate increasing with an increase inchamber pressure, at least up to 20 mT.

Curve 320 of FIG. 3B shows the etch rate 322 as a function of plasmasource power 324, with the etch rate increasing with an increase inplasma source power, at least up to 1,600 W.

Curve 330 of FIG. 3C shows the etch rate 332 as a function of bias power334, with the etch rate slightly decreasing with an increase in biaspower, at least up to 600 W. This is an unexpected result It may be thatthe higher bias power is causing the deposition of a species at thesurface of the patterned spaces where etching is occurring, and thisspecies is inhibiting the etching of the copper. However, by adjustingother variables such as process chamber pressure and plasma sourcepower, the shape of this curve may be altered.

We also investigated the variable of feed gas composition, where thesccm of HCl was decreased to 75 or 50 or 25 sccm with other feed gasflow rates held almost constant at the values previously specified foran HCl flow rate of 100 sccm. We discovered that the etch rate was onlymarginally affected, with a slight increase in etch rate with increasingHCl flow rate. Based on this discovery, we have concluded that, for HClflow rates above about 25 sccm (and under the process conditionsdescribed), it is the surface reaction rate which controls the etchrate, rather than the concentration of reactive species in the plasma orthe transfer rate of those species to the surface of the copper.

EXAMPLE TWO Selectivity

We have determined that, using the substrate and process variablesspecified with reference to FIG. 2A, the selectivity ratio of copper tosilicon oxide hard mask is about 4:1 (i.e., copper etches four timesfaster than the hard mask).

Further, the effect of process variables on this selectivity wereinvestigated. In particular, the effect of process chamber pressure,plasma source power, and bias power were investigated. Again, HCl wasthe principal source of etchant reactive species; the plasma feed gaswas of the composition specified with reference to FIG. 3A above; thesubstrate stack was the same; the pattern etched was the same; and allprocess variables were the same with the exception of the variableinvestigated.

Curve 410 of FIG. 4A shows the selectivity ratio 412 of copper tosilicon oxide hard mask as a function of process chamber pressure 414,with the selectivity ratio increasing with an increase in chamberpressure, at least up to 20 mT.

Curve 420 of FIG. 4B shows the selectivity ratio 422 as a function ofplasma source power 424, with the selectivity ratio increasing with anincrease in plasma source power, at least up to 1,600 W.

Curve 430 of FIG. 4C shows the selectivity ratio 432 as a function ofbias power 434, with the selectivity ratio decreasing with an increasein bias power, at least up to 600 W.

Again, we investigated the effect of varying feed gas composition, wherethe sccm of HCl was decreased to 75 or 50 or 25 sccm with other feed gasflow rates held essentially constant at the values previously specifiedfor an HCl flow rate of 100 sccm. We discovered that the selectivityratio for copper to silicon oxide hard mask was relatively unaffected.

EXAMPLE THREE Comparative Example

As previously described, we have determined that the etch processtypically applied to aluminum does not work well for copper. This is notto say that such a process cannot be made to work if all of thevariables are carefully optimized. However, the method of the presentinvention offers a wider process window.

In reviewing the March 1995 article “Dry Etching Technique forSubquarter-Micron Copper Interconnects” by Igarashi et al. where theetch process recommended is a variation of the process used foraluminum, we noticed that the interior of the etched copper featuresappeared to be hollow at some locations. To determine the cause of thisphenomenon, we attempted to reproduce the results of Igarashi et al.This example is provided as a comparative example, since the process wascarried out in the same equipment in which we achieved the eliminationof the interior corrosion of the copper features.

The particular etched substrate illustrated in FIGS. 5A and 5B wasprepared as follows: The substrate was a silicon wafer overlaid by asilicon oxide layer; a tantalum barrier layer about 500 Å thickoverlying the silicon oxide surface; a layer of sputter-deposited copperabout 5,000 Å thick overlying the tantalum barrier layer; a 250 Å thicktantalum layer overlying the copper layer; and, a 5,000 Å thickpatterned silicon oxide hard mask overlying the tantalum layer.

The plasma feed gas comprised 100 sccm Ar, 20 sccm Cl₂, 15 sccm N₂, and10 sccm BCl₃. A relatively high concentration of N₂ and a higher biaspower during etching were used to for a thicker passivation layer on thesidewall.

The RF plasma source power was approximately 1,500 W. The bias power wasapproximately 500 W. The pressure in the etch chamber was about 10 mT.The temperature on the substrate surface was about 200° C., while thewall temperature of the etch chamber was about 80° C.

FIGS. 5A and 5B are schematics of photomicrographs of the etched patternof 0.5 μm lines 510 and spaces 512 created by the method describedabove. With reference to FIG. 5A, the silicon oxide hard mask 514overlies tantalum barrier layer 515. The etched copper lines 510 includethe copper 520 remaining after etch, surrounded by vacant space 522where the copper has reacted with a corrosive agent to produce avolatile species which escaped into the process chamber. The exteriorwalls 516 of the etched copper have been passivated so that they remainrelatively intact despite the corrosion of the interior of the copperline 510. The silicon oxide surface 518 of the etched spaces 512 isrelatively free from contaminating deposits.

FIG. 5B shows the problem of the corrosion of the interior of the etchedlines 510 in more detail. Again, the silicon oxide hard mask 114 setsabove tantalum barrier layer 515. The copper line exterior walls 516 areapparently continuous and intact However, interior to the walls 516, thecopper 520 has been corroded and the reactive species resulting from thecorrosion have escaped leaving open space 522 surrounding the corrodedcopper 520.

EXAMPLE FOUR A Preferred Embodiment of the Present Invention

As disclosed in the Summary of the Invention, the preferred embodimentof the invention provides for the use of hydrogen chloride (HCl) and/orhydrogen bromide (HBr) as the sole or principal source of the reactivespecies used in etching copper. Dissociation of the HCl and/or HBrprovides the large amounts of hydrogen necessary to protect the copperfeature etched surfaces from penetration by reactive species adjacentthe etched surface. Additional hydrogen-comprising gas may be added tothe plasma feed gas which comprises the HCl and/or HBr when the reactivespecies density in the etch process chamber is particularly high.

In this example, under the conditions specified, it is not necessary toadd additional hydrogen-comprising gas to the plasma feed gas. Althoughthis Example is for the use of HCl as the principal source of reactivespecies, HBr could be substituted in this example with equivalentresults.

In this Example, the plasma feed gas consists of HCl at a flow rate ofabout 100 sccm, N₂ at a flow rate of about 20 sccm and BCl₃ at a flowrate of about 5 sccm, where the chemically reactive copper etchant wasHCl, the N₂ was used to passivate silicon species (and some copperspecies), and the BCl₃ was used to scavenge oxygen generated by etch ofthe silicon hard mask or the silicon oxide dielectric layer underlyingthe copper line. In addition, we have evaluated varying ratios of theplasma feed gas components, such as: 50 sccm HCl and 5 sccm N₂; 50 sccmHCl, 25 sccm N₂, and 5 sccm BCl₃; 50 sccm HCl, 5 sccm N₂, and 5 sccmCHF₃; and, 100 sccm HCl, 5 sccm N₂, and 5 sccm BCl₃. We also evaluatedHCl as the sole plasma feed gas at 50 sccm of HCl. In evaluating all ofthese plasma feed gases, we learned that we could produce a patternedetch of 0.5 μm wide lines and spaces where etch rate, selectivity,feature dimensions, and feature integrity are all excellent. In fact,the etch results were so similar, that FIGS. 6A, 6B, and 6C whichrepresent this Example are representative of the features obtained forall of the plasma feed gas combinations evaluated, including HCl as thesole feed gas.

The substrate etched was a silicon wafer overlaid by a silicon oxidelayer; a tantalum barrier layer about 500 Å thick overlying the siliconoxide surface; a layer of sputter-deposited copper about 5,000 Å thickoverlying the tantalum barrier layer; 250 Å thick tantalum layeroverlying the copper layer; and a 5,000 Å thick patterned silicon oxidehard mask overlying the tantalum layer.

The RF power to the plasma induction coil, the plasma source power, wasabout 1,500 W @ 2 MHz, and the RF power to the substrate support platen,the bias power, was about 500 W @ 13.56 MHz. The pressure in the processchamber was 20 mT. The substrate temperature was about 200° C. and thewall temperature of the process chamber was about 80° C. Etching wascarrier out over a time period of about 100 seconds.

FIGS. 6A and 6B are schematics of photomicrographs of the etched patternof 0.5 μm lines 610 and spaces 612 created using the method describedthis Example Four. With reference to FIG. 6A, the silicon oxide hardmask 614 overlies tantalum barrier layer 615. The etched copper lines610 include the solid interior copper 620 remaining after etch. Theexterior walls 616 of the etched copper are deposit free and exhibit thedesired profile which is achieved by the anisotropic etch processdescribed above. The silicon oxide surface 618 of the etched spaces 612is also free from contaminating deposits.

FIG. 6B shows a schematic of the cross-sectional view of the lines andspaces of FIG. 6A. Again, the silicon oxide hard mask 614 sets abovetantalum barrier layer 615. The copper line exterior walls 616 are freeof deposits from the etch process. In addition, the interior copper 620solidly fills the exterior walls 616, providing a line 610 structurehaving integrity.

By comparison with the line 510 structure from the Comparative ExampleThree, the absence of corrosion in the interior copper 620 of thepreferred embodiment described in this Example Four is attributed to thegeneration of hydrogen upon dissociation of the HCl plasma feed gas. Thehydrogen is believed to absorb on the surface of the copper, forming anH-rich layer. This H-rich layer reduces, and typically prevents reactionof the copper with Cl or Cl₂ by forming volatile HCl. Thus, the hydrogenpresent on the copper surface acts as a buffer which permits etching tooccur without leaving behind excess chlorine on the copper surface whichcauses continuing undesired reaction with the copper after the desiredetch is completed. It is this continuing undesired reaction, combinedwith the formation of copper oxides, which we are calling “corrosion”.It is corrosion which generates vacant spaces (of the kind shown inFIGS. 5A and 5B) inside the walls of the copper lines.

FIG. 6C shows schematic of a photomicrograph of the FIG. 6A etchedcopper pattern. The photomicrograph shows the top surface 630 afterremoval of the silicon oxide hard mask, the walls 616 of the etchedlines 610, and the silicon oxide surface 618 of etched spaces 612, toillustrate the absence of any deposits on these surfaces.

Once the non-corroded etched feature is created, a capping layer can beapplied to the copper surface to prevent future corrosion. Preferredcapping layers include silicon nitride and silicon oxynitride. Thesecapping layers can be generated by adding nitrogen and/or anitrogen-containing gaseous compound to an inert carrier gas, forming aplasma, and plasma sputtering against a silicon oxide-containingsurface, such as a silicon oxide hard mask.

Although specific process conditions are described with respect toExample Four above, applicants have learned that the process window isquite broad and that the process variables can be adjusted over a widerange and still provide excellent etched copper features.

For example, the plasma source power supplied for production of reactivespecies (ions and neutrals) may vary widely. The minimum power requiredis the power necessary to break down HCl or HBr into several reactivespecies, such a H, excited H, H⁺, Cl, excited Cl, Cl⁺, excited HCl,HCl⁺, Br, excited Br, and Br⁺. Often the minimum power required is thepower to ignite and sustain the plasma in the process chamber. In a DPSchamber of the kind we used, the minimum inductive RF power required isgenerally about 200 W @ 2 MHz. However, the power supplied may rangefrom about 200 W to about 2,500 W, depending on the feature to beetched, the materials involved, and the make up of the plasma feed gas,for example. In addition to dissociation and ionization of the plasmafeed gas, the RF power sustaining the plasma is also a source ofsupplying heat to the wafer surface (the higher the power, the higherthe wafer temperature). The RF power also affects the production of UVlight and/or IR light which is generated from the plasma These lightsources may impact the reaction taking place on the substrate surface.

It is important to note that the plasma source power may be suppliedfrom varying types of equipment, including: a parallel plate plasmasource; an inductive coil, whether that coil is located externally tothe process chamber, internally to the process chamber, or a combinationof both; and a microwave plasma source (by way of example and not by wayof limitation).

The bias power used to control ion bombardment on the substrate surfacemay also be varied over a range depending on the feature to be etched,the materials involved, and desired characteristics of the semiconductordevice in general. The minimum bias power required for the HCl and HBretch chemistry described herein is the power which can provide thedesired ion directionality and ion bombardment energy for an anisotropicetch. In a DPS chamber of the kind we used, the minimum RF powerrequired is generally about 50 W @ 13.56 MHz. However, the RF powersupplied may range from about 50 W to about 800 W, depending on thefeature to be etched, the materials involved, and the make up of theplasma feed gas, for example. Higher bias power typically increases theetch rate due to the higher ion bombardment energy; however, as shownwith regard to Example 1, FIG. 3C, this is not necessarily the case.Higher bias power may result in the generation of additional specieswhich affect etch rate. Bias power also affects the dimensionality,including the etch profile of the feature being etched, and must beadjusted as required to obtain proper feature dimensions. Higher biaspower also results in an increase in the temperature of the substratesurface as a result of increased ion bombardment and may require a meansfor cooling of the substrate during the etch process.

Process chamber pressure variation, all other variables held constant,may affect the dissociation rate, ionization rate, and recombinationrate of various plasma feed gases. It is possible to optimize thereactive species generated and to control the ratios of the etchantspecies using process chamber pressure. Thus, both passivation and etchrates can be adjusted using process chamber pressure. Pressure may alsoaffect the thickness of the plasma sheath within the reactor and therebythe ion bombardment energy. The optimal process chamber pressure isequipment sensitive. In a DPS chamber of the kind we used, the optimalpressure appears to be about 20 mT. However, we have operated theprocess chamber at pressures ranging from about 5 mT to about 40 mT andachieved acceptable etch results.

The surface temperature of the substrate affects the reaction rates onthat surface and the dissociation rate of etch by-products. When copperis etched using HCl or HBr, or a combination thereof as the principalsource of the reactive etchant species, desorption of the etch-byproductappears to be more critical than surface reaction rate, and it appearsthat a minimum substrate surface temperature of about 150° C. providesthe necessary desorption rate.

Although the preferred embodiments described are with reference to anetching process where the composition of the plasma feed gas wasconstant throughout, one skilled in the art would appreciate that thefeed gas could be varied during an etching process and the method of thepresent invention could be used for a limited time period during thatetching process.

The above described preferred embodiments are not intended to limit thescope of the present invention, as one skilled in the art can, in viewof the present disclosure, expand such embodiments to correspond withthe subject matter of the invention claimed below.

We claim:
 1. A method of patterning a metal film on a substrate surfacefor use in semiconductor applications, wherein said patterning isaccomplished by plasma etching, said method comprising: placing asubstrate including said metal film on a substrate support pedestalwithin a plasma etch process chamber; supplying a halogen-comprisingplasma feed gas to said plasma etch chamber to generate an etchantplasma, wherein at least 40% of the total reactive species present insaid etchant plasma are generated from a feed gas selected from thegroup consisting of HCl, HBr, and combinations thereof, and wherein 30%or less of other plasma-generated reactive species provide surfacepassivation of etched metal surfaces during etching of said metal film,whereby components of said plasma feed gas enable the application ofsufficient hydrogen to an etched portion of a metal feature surface toprotect said etched portion of said metal feature surface from reactionwith reactive species during etching of an adjacent feature surface;using said plasma feed gas to generate a plasma; exposing said substrateto said plasma; and applying a heat transfer gas to a backside of saidsubstrate during said patterning, to achieve and maintain said substratesurface at a temperature ranging from about 130° C. to about 300° C. 2.The method of claim 1, wherein said heat transfer gas is a chemicallyinert gas.
 3. The method of claim 2, wherein said inert gas is helium.4. The method of claim 1, wherein at least 50% of the total reactivespecies present in said etchant plasma are generated from a portion ofsaid feed gas which comprises said HCl, HBr, and combinations thereof.5. The method of claim 1, wherein said halogen-comprising feed gas alsocomprises hydrogen.
 6. The method of claim 1 or claim 5, wherein saidmetal film comprises copper.
 7. The method of claim 6, wherein saidmetal is copper and said pattern includes a feature having a criticaldimension of 0.5 μm or less in size.